Abstract

Engineered nanoparticles (ENPs) find large scale industrial application because of their promising chemical, physical, electrical, magnetic, optical, and electronic properties. Copper-based ENP are used as gas sensors, in catalysts, electronics, semi-conductors, and in agriculture. They have been useful as agricultural amendments in the form of pesticides, herbicides, and fertilizers because of their antifungal and antibacterial properties. They also find application in electronics and sensors used in precision agriculture. Due to their massive production and use, ENPs are likely to be ubiquitous in the environment around us in the near future. Application of biosolids for fertilization and water from wastewater treatment plants for irrigation are other possible routes of ENP exposure to plants. Several studies have shown that copper-based ENPs disturb plant physiology and development; however, practically no work and very little work has been done on bell pepper (Capsicum annuum) and spinach (Spinacia oleracea) plants. Bell pepper is a worldwide consumed vegetable very rich in carotenoids, especially zeaxanthin, a powerful antioxidant. Spinach is another important vegetable consumed widely across cultures as a source of iron and pro-vitamin A. This research project is aimed to understand the effects of copper based compounds on bell pepper plants at half and full life cycle. It also analyzes the effects of soil weathering of the copper based nanoproducts on spinach plants. The investigation included three parts. The very first part consisted of culturing bell pepper plants until reaching physiological maturity (90 days), in soil amended with nano CuO (nCuO), bulk CuO (bCuO), and ionic copper (CuCl2) at 0, 125, 250, and 500 mg/kg. Ionic copper significantly decreased the gas exchange parameters, evapotranspiration, stomatal conductance, and photosynthesis by an average of 41 %, 59%, and 38%, respectively, compared to the other treatments at select concentrations (p ≤ 0.05). Except for bCuO at 500 mg/kg, at 250 mg/kg and above, the three compounds significantly increased root Cu (196%, 184%, and 184%), respect to control. Only 500 mg/kg ionic Cu gave significantly higher root Cu compared to the other Cu treatments. Additionally, at 125 mg/kg, leaf P was 41% lower for nCuO, against the bCuO treatment. At 500 mg/kg, nCuO reduced Zn by 55% in leaf and 47% in fruit, compared to control (p ≤ 0.05). The second part encompassed the evaluation of nCu and bCu species on agronomical and biochemical traits of bell pepper plants. This part was conducted in 2 phases, namely, vegetative stage [(VS)/half life cycle study (45 days)] and reproductive stage [(RS)/full life cycle study (90 days)]. Thirty day-old seedlings were transplanted into soil amended with 0 (control), 62.5, 125, and 500 mg Cu/kg and evaluated at the two phenological stages. At the VS, plants exposed to 500 mg nCu/kg had longer (58%) and heavier (187%) roots, compared to control (p ≤ 0.1). At such growth stage, all plant tissues showed significantly higher Cu concentration from bCu treatments. Contrarily, at RS, Cu concentration in leaves of plants exposed to 500 mg nCu/kg was higher by 1510%, compared to bCu (p ≤ 0.05). Additionally, 500 mg/kg nCu increased photosynthesis (42%) and stomatal conductance (51%), while 62.5 mg/kg increased evapotranspiration (31%), compared to bCu counterpart (p ≤ 0.05). In the third part, the ENPs were weathered/aged for 5 weeks in soil before spinach seedling transplantation. The resultant effects on the agronomical, physiological, and biochemical parameters, especially on the nutrient quality were evaluated. Plants were exposed for five weeks to freshly prepared or soil-aged (35 days) nCuO, bCuO, or CuSO4 suspensions/solutions at 0 (control), 400, 400, or 40 mg/kg, respectively. Foliar health, gas exchange, carotenoid, chlorophyll, catalase and ascorbate peroxidase enzymes, as well as element bioaccumulation were evaluated. Foliar biomass was higher in UW control (84%) and in UW ionic treatment (87%), compared to the corresponding W treatments (p ≤ 0.1). Shoot Cu bioaccumulation for both W and UW (nano and bulk) CuO were significantly higher than control but showed no effect of weathering. No significant differences were observed in the root Cu bioaccumulation. At 40 days post transplantation, the intercellular CO2 concentration was lower by 28% for W nCuO treatment, compared to W control (p ≤ 0.1). Root catalase activity was higher by 110% in UW bCuO treatment, compared to the W counterpart; it was also higher for W ionic treatment by 216%, compared to the UW one (p≤ 0.05). At 20 days post transplantation, W nCuO gave 56% and 57% lower carotenoid, compared to W control and to UW counterpart, respectively (p ≤ 0.05). At 10 day exposure period, Chl a for UW control was higher by 72% than W control (p ≤ 0.05); conversely, at 30 days, it was higher for W by 91% than the UW control (p ≤ 0.05). This work was especially focused on the nutritional quality of the fruit/leaf, since that is the portion of plant consumed by humans. The findings indicate that depending on the plant species, growth media, and specific dosage of copper-based ENPs, they could be beneficial or detrimental to plant health.